Protective efficacy of a hypothermic pharmacological agent in gerbil forebrain ischemia.

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Abstract
The novel muscarinic cholinergic partial agonist U-80816E was tested in the gerbil brief bilateral carotid occlusion ischemia model based on the rationale that the compound's hypothermic properties might afford effective protection of the selectively vulnerable hippocampal CA1 region. Male gerbils were subjected to either 10 or 15 minutes of bilateral carotid occlusion, followed by histopathological assessment of the CA1 neuronal survival 7 days later. In saline-treated animals, 10 minutes of bilateral carotid occlusion resulted in a 30.5% loss of CA1 neurons, whereas a 15-minute insult resulted in a 49.6% loss. Administration of U-80816E (6 mg/kg i.p. 30 minutes before bilateral carotid occlusion and again 2 hours after reperfusion) resulted in a significant protective effect of the CA1 neuronal population with either duration of ischemia; neuronal loss was reduced to 12.6% in the milder model (p < 0.05 versus saline-treated) and 24.9% in the more severe model (p < 0.04 versus saline). However, the 6 mg/kg i.p. dose of U-80816E was found to produce a 1.0 degree C decrease in brain temperature (measured with a tympanic temperature probe) at 10 minutes of ischemia compared with that of saline-treated gerbils. At 10 minutes of reperfusion, after the 10-minute episode of ischemia, the brain temperature of the U-80816E-treated gerbils was 2.2 degrees C lower than that of saline-treated animals. When the U-80816E-treated gerbils were subjected to either 10 or 15 minutes of ischemia but placed in a heated chamber that prevented the hypothermic effects, no cerebroprotection was observed. These results show that the anti-ischemic efficacy of U-80816E is mediated through its hypothermic properties, thus suggesting the feasibility of pharmacologically induced hypothermia as a cerebroprotective approach.